Diffusion of colloidal pairs and aggregates

Question

I understand that the diffusion of individual colloidal particles of a dilute suspension is described relatively well through Stokeslet analysis of the fluctuating microscopic flows that generate (or are generated by) movement of those particles. Does this approximation become intractable when the particles are in close proximity or in contact? If so, is there another perturbative or non-perturbative framework for estimating the diffusion operator of colloidal aggregates?